The purpose of this project is to study the pathology, diagnostic features, clinical manifestations, and epidemiology of mousepox caused by the 1979 NIH isolate of ectromelia virus. The specific areas of interest include 1) comparison of histopathology with that produced by other strains of virus, 2) effect of ectromelia on nude mice, 3) application of immunocytochemical methods for demonstration of viral antigen in tissues, and 4) study of the spread of the virus and clinical features of the disease in an isolated colony of experimental mice.